A fairly simple thing, but if you are using disposable nappies, buy in bulk when there are sales on! It works out HEAPS cheaper and means you don't buy nappies anywhere near as frequently at more expensive prices!

Also, if you are formula feeding and are going out, take hot water in the bottle and the formula in a formula dispenser to make up your bottle fresh. This way if baby doesn't end up needing a bottle whilst you are out, you only end up throwing out the water, not the formula!! Formula can be expensive (depending on the brand you use) so you don't want to waste it!